Xerographic system

ABSTRACT

AN ELECTRICALLY CONDUCTIVE YET ELECTRONIC CHARGE CARRIER BLOCKING INTERFACE COMPRISING GRAPHITE BETWEEN A SUPPORT BASE AND PHOTOCONDUCTIVE INSULATING MATERIAL OF A XEROGRAPHIC PLATE, AND A PROCESS OF MAKING AND USING THE PLATE.

Much 1974 N. L. PETRUZZELLA 3,799,775

XEROGRAPHIC SYSTEM Original Filed Sept. 21, 1967' United States PatentOflice 3,799,775 Patented Mar. 26, 1974 3,799,775 XEROGRAPHIC SYSTEMNicholas L. Petruzzella, Columbus, Ohio, assignor to Xerox Corporation,Rochester, N.Y. Continuation of abandoned application Ser. No. 669,477,Sept. 21, 1967. This application July 13, 1972, Ser. No.

Int. Cl. G03g 5/00 U.S. Cl. 96--1.5 8 Claims ABSTRACT OF THE DISCLOSUREAn electrically conductive yet electronic charge carrier blockinginterface comprising graphite between a support base and photoconductiveinsulating material of a xerographic plate, and a process of making andusing the plate.

CROSS REFERENCE TO RELATED APPLICATION This is a continuation ofapplication Ser. No. 669,477, filed Sept. 21, 1967, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to xerography and inparticular to novel xerographic plates, their fabrication and their usein xerography.

In the process of xerography, for example, as disclosed in Carlson Pat.2,297,691: a xerographic plate comprising a layer of photoconductiveinsulating material on an electrically conductive backing is given auniform electric charge over its surface and is then exposed to a lightand shadow image pattern of the subject matter to be reproduced, usuallyby conventional projection techniques. This exposure discharges theplate areas in accordance with the radiation intensity that reaches themand thereby creates an electrostatic latent image on or in thephotoconductive layer corresponding to the light and shadow imagepattern. Development of the latent image is effected with anelectrostatically charged, finely divided material, such as anelectroscopic powder, that is brought into surface contact with thephotoconductive layer and is held thereon electrostatically in a patterncorresponding to the electrostatic latent image. The developed,xerographic marking material image may be fixed or made permanent on thexerographic plate itself. Alternatively, if it is desired, to apply thedeveloped xerographic powder image to paper, metal foil, plastic film orother transfer material, the developed image may be transferred from thexerographic plate to such a support surface to which it may be afixed byany suitable means. Fixing of the developed image onto the xerographicplate itself becomes attractive for relatively inexpensive plates suchas those comprising photoconductive material impregnated into paper.Illustratively, paper may be impregnated, by melting or from solution,with organic or inorganic photoconductive materials, such as anthi'aceneor sulfur. It is also well-known, in the art, that materials such aszinc oxide in a binder may also be used as a photoconductive layer onpaper. See Young, C. 1., and Greig, H. 6., RCA Review, 15, No. 4, 471(1954) and Thomsen Pats. 2,727,807 and 2,727,808. Said Carlson patentalso relates that a paper backed xerographic plate may be layered withconductive material such as bronze or carbon powder held in a hinder,the photoconductive insulating material then being applied to theconductive surface.

However, as is known by those skilled in the art, it is generally foundto be preferred to interpose a thin, in the region of from about 25angstorm units to 2 microns thick, layer of insulating material betweenthe conductive backing and the photoconductive insulating layer inxerographic plate construction in order to increase the ability of theplate to hold a charge in the dark without adversely affecting theplates ability to rapidly dissipate charge in light struck areas. In theart such layers are called barrier layers because they serve as abarrier between the charged photoconductor and the electricallyconductive substrate to prevent or retard the dissipation of charge inthe dark and thereby prevent the loss of charge from the plate at leastduring the period between the time of charging of the plate and exposureto an image to be copied and between the time of forming the latentelectrostatic image and image development. The effect of such thinelectrically insulating interfaces in xerographic plates is more fullydescribed in Dessauer et a1. Pat. 2,901,348.

Dielectric barrier layers are not entirely satisfactory since they mustbe kept extremely thin to minimize the build up of a residual potentialin the barrier layer which, .in recycled reusable xerographic plates,undesirably, raises the background development level and lowers contrastand resolution of resultant xerographic prints.

Also, commercially used interfaces often take the form of a thin layerof the oxide of the metal substrate of the xerographic plate, forexample, aluminum. These oxide, insulating interfaces are often found tobe fragile and subject to local defects, due to thin spots, cracks,discontinuities, or chemical impurities which give rise to powderdeficient spots and other print imperfections. This tendency to degradeis, of course, aggravated by prolonged cycling conditions which modernway xerographic copiers are being increasingly subjected to. Therequirement of avoiding these localized failures makes it ditficult touse such well known blocking layers as aluminum oxide over aluminumsheet, because of their fragility under belt flexing conditions. This isunfortunate because belts made of metals such as brass and aluminum,otherwise possess the desired mechanical properties required in flexiblexerographic belt operation.

In addition, such thin insulating barrier layers are found to beunsatisfactory over such highly injecting substrates such as brass andsimilar alloys which mechanically and otherwise are highly desirablesubstrates especially for continuous flexible web xerographic members,because of the significant decrease in charge acceptance of the memberas in prolonged cycling found when these substrates are used with suchimportant photoconductors as those comprising amorphous selenium orphthalocyanine enamels further as described in copending applicationSer. No. 375,191, filed June 15, 1964, now abandoned.

Also, since the previously known dielectric barrier layers used on brasshad to be extremely thin in order to minimize residual potential, theycould not serve as elfective chemical barrier layers between seleniumand the brass substrate and specialized barriers such as chromateinterfaces, for example, see copending application Ser. No. 341,774,filed Jan. 31, 1964, now U.S. Pat. 3,352,669, had to be resorted to toprevent the gradual contamination of the amorphous selenium by thesubstrate. This contamination was found to substantially degrade theelectrical properties of the plate if the plate was aged a few months.Especially drastic was the decrease in charge acceptance brought aboutby this contamination.

Generally, in xerographic plate fabrication, preferred photoconductiveinsulating materials, for example, those comprising amorphous selenium,have been deposited upon rigid backing materials such as flat plates orrigid cylindrical drums and it is found that using ordinary cleaningprocedures for the substrate, the physical bond existing between thesupporting base or substrate and the deposited photoconductor issufficient to ensure an adequate commercial life for the xerographicplate.

However, in order to increase the speed of commercial xerographiccopiers, interest has recently been shown in going from the rigidlybacked plate to a xerographic plate wherein the backing takes the formof a flexible belt, for example, similar to the one shown in Clark etal. Pat. 3,146,688. Such a plate configuration and variations thereofoffer an increased reproduction surface thereby permitting an increasedrate of reproduction of copies from an original.

However, the use of such a flexible belt system has a number ofattendant problems. A major problem is one of obtaining sufficientadhesion of photoconductor to the belt base since it is found that thecontinuous flexing of the photoconductive layer as it is passed around,for example entraining pulleys or rollers, often leads to cracks andseparation of the photoconductor from the base. In addition, suchrelatively frangible but preferred photoconductors such as amorphousselenium optionally doped with various additives or mixed with variousother materials such as arsenic and tellurium suffer even more fromcracking and spalling or flaking problems due to flexing and otherstrains including those produced by differences in thermal expansionbetween the backing or substrate and the photoconductive layer. Axerographic plate in a commercial machine may be subjected to asubstantial temperature difference between 0001 periods when out of useand unavoidable heating due, for example, to the proximity of a thermalfuser to fuse the transferred toner image.

There is also the problem of the mechanical and electrical discontinuityat the connecting seam of a supporting flexible belt substrate.Continuity is necessary to provide for uniform quality prints evenacross the seam. Belt bases may be connected at the seam, for example,by welding, soldering, glueing or other connecting means. The seamproduced by present belt fabrication methods seriously complicatesmachine design since the seam portion is often left uncoated or unevenlycoated with photoconductor, using present coating methods, and hencethese areas will not print or if coated the electrical and xerographicproperties, particularly insofar as dark charge injection is concerned,are effected by the solder or adhesive used to join the ends of thesupport together to form a belt. Also, the seam is thicker than the beltthickness and thus close processing tolerances required for optimumfharging, electrode development and so on, must be reaxed.

These problems have been approached in copending application Ser. So.579,826, filed Sept. 16, 1966, now abandoned, wherein a resinousinterfacial layer of about 0.1 to about 5 microns thick is deposited onan electrically conductive substrate and the photoconductive materialdeposited thereover. Satisfactor bonding and electrical characteristicshave been obtained using this approach but a characteristic of thisteaching is that the interfacial layer, because it generally has anelectrical resistivity of between about -40 ohm-centimeters, dictated bythe resistivities of the resins used, must be deposited on anelectrically conductive substrate in order to ensure the rapiddissipation of charge from light struck areas of the plate. This meansthat a belt like support layer which is not electrically conductive mustfirst be layered with an electrically conductive layer which can be acostly and difficult to control process. Such a process also generallyleaves the scam in the underlying belt substrate as a discontinuity evenafter deposition of the electrically conductive layer. In addition, thisinterfacial layer is electricall insulating and may suffer from theinherent disadvantages of such insulating layers, as pointed out herein.

Also, in copending application Ser. No. 578,502, filed Sept. 12, 1966,now abandoned, it is suggested that an interfacial adhesive coating ofabout 0.5 to about 5 microns of a photoconductive phthalocyanine pigmentin an insulating resin binder be coated on the electrically conductivesubstrate and this interfacial binder then be overcoated with thephotoconductor amorphous selenium. In this approach also the substratemust be electrically conductive. Also, an interface of a particularphotoconductive insulating material with a particular photoconductoroverlayer are specified. Also, in both of the mentioned copendingapplications, the maximum thickness of the interfacial layer is quitethin necessitating carefully controlled layering techniques.

Also, unless the interfacial layer also serves as an effective barrierlayer, then the fabrication of a flexible belt type xerographic plate isfurther complicated by the requirement of depositing such a barrierlayer over the interfacial layer during plate fabrication.

Thus, it is seen there is a continuing need for an inexpensive, simpleand workable system to provide for a xerographic plate and especially aflexible belt type xerographic plate with acceptable mechanical andelectrical characteristics.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide a xerographic plate and a method of fabricating and usingsame which overcomes the above-noted disadvantages and satisfies theabove-noted wants.

It is a further object of this invention to provide a layer backing thephotoconductor in a xerographic plate which serves both as anelectrically conductive layer and, surprisingly, additionally serves asan excellent barrier layer over electronic charge carrier injectingmetals.

It is a further object of this invention to provide an interfacialcoating permitting photoconductive insulating materials to tenaciouslyadhere to a support base especially during bending and flexing of thebase irrespective of whether the base is electrically conducting orinsulatmg.

It is a further object of this invention to provide a barrier layerwhich is not subject to oxidation and chemical change during storage andoperation.

It is a further object of this invention to provide a xerographic platewith excellent adhesion of the photoconductor to a wide variety ofsupport bases.

It is a still further object of this invention to provide a xerographicplate fabricating method that permits fabricating flexible belt typephotoconductors on pre-formed belt bases fabricated in a conventionalmanner.

It is a still further object of this invention to provide a flexiblebelt xerographic plate fabricating method which eliminates electricaland mechanical discontinuities at the support base seam.

It is a still further object of this invention to provide an interfacebetween a photoconductor and a base which is thought to permit minuteslipping of photoconductor relative to the base to prevent cracking andspalling of the photoconductor.

It is a still further object of this invention to provide an interfacebetween a photoconductor and a base, the interface comprising a materialconventionally known as a lubricant but which, as used herein actuallyimproves the adhesion of the photoconductor especially during bendingand flexing of the base.

The foregoing objects and others are accomplished in accordance withthis invention by providing an interface comprising predominantly (atleast 50% by weight) the material known as a lubricant, namely graphitebetween a support base and an overcoated photoconductor of a xerographicplate to unexpectedly improve the adhesion of the photoconductor to thebase while simultaneously providing a layer which is both electricallyconductive and unexpectedly electronic charge carrier blocking.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of theinvention as well as other objects and further features thereof,reference is made to the following detailed disclosure of this inventiontaken in conjunction with the accompanying drawing showing a schematic,partially sectional view of an embodiment of an automatic xerographiccopying apparatus employing a Xerographic plate according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventive xerographicplates of the present invention are preferably prepared by applying thegraphite to a pre-formed xerographic plate base and applying thereover alayer of photoconductive insulating material, in a manner to bedescribed, to optimize the adhesive and the other mechanical propertiesof the inventive interlayer and to optimize as well the electricalproperties including the electrically conductive yet effective barrierlayer characteristics of the interface. It was by no means expected orobvious that a graphite interlayer should act as its own effectiveblocking layer, requiring no added dielectric layer to preventsubstantial dark injection of carriers from the electrode into thephotoconductive insulator. Since, once it is coated with graphite, thesupport may be selected without concern for its electrical properties,the latter may be either a conductor, such as a brass belt, or a plasticdielectric, such as Mylar.

While this invention is particularly applicable and advantageous infabricating flexible belt type xerographic plates it should be notedthat the invention is entirely applicable to rigid substrates eventhough the problem of constant flexing is not present and the adhesiveadvantages of the invention may not be completely appreciated.

Referring now to the figure, there is shown automatic xerographiccopying apparatus 1. The apparatus is seen to include a pair of rollersand 11 about which is supported a xerographic plate 12 in the form of anendless flexible belt comprising, according to the invention, basicallythree layers, an overlying layer of photoconductive insulating material7, a graphite interfacial layer according to the invention 8 andflexible belt support layer 9. Layer thicknesses are exaggerated forpurposes of illustration.

Because of the invention herein, belt base 9 need not be electricallyconductive as was required in the prior art. Especially preferredelectrically conductive substrates because of the excellent adhesion ofthe graphite to the base are brass, steel and aluminum, for example,cold rolled and from about 2 to 10 mils thick. Any suitable electricallyconductive belt base may be used. However, any suitable electricallyconductive or insulating support material may be used. Typicalelectrically conductive supports include plastic webs such as aluminizedpolyethylene terephthlate polyester film, the polyester film availableunder the trademark Mylar from Du Font and other metals. Especiallypreferred electrically insulating substrates because of the excellentadhesion of the graphite to the base are acrylics especially if theplastic is vapor tackified prior to application of the graphite, paperincluding ordinary bond and cardboard, polycarbonate, cellulose acetate,polypropylene, rubber and polyvinyl chloride foam. Typical electricallyinsulating supports include paper, plastics, rubbers, film formablepolymeric materials other than Mylar, for example, see a partial list incopending application Ser. No. 598,279, filed Dec. 1, 1966, now US. Pat.3,519,124, woven or non-woven fibrous cloth belts, for example of glass,cotton, flax, silk or like fibers or fibrous resin belts, for example ofacrylonitrile, polyester, nylon, rayon, acetate and tri-acetate,ethylene, propylene or other olefins, polycarbonate or like fibers whichbelts may optionally be impregnated with a flexible resin or polymerictype material.

The inventive interlayer 8 may comprise solely particulate graphite forexample when applied to base 9 in a fugitive carrier or may compriseparticulate graphite 'in a suitable non-fugitive carrier, so that thelayer desirably has an electrical resistivity less than about 10ohmcentimeters and preferably less than about 10 ohm-centimeters inorder to dissipate charge from the photoconductor in illuminated areas.

Carrier liquids may be used to provide for layer 8. Any suitable carrierliquid capable of having graphite in finely powdered, flaked or otherparticulate form dispersed therein for example in a dispersion and whichare capable of being coated or layered on a pre-formed belt base to forman adhesive coating for an overcoating of a photo conductor as describedmay be used.

Graphite may be incorporated in the liquid carrier by any suitable meanssuch as strong shear agitation preferably with simultaneous grinding.These methods also include ball milling, roll milling, sand milling,ultrasonic agitation, high speed blending, and any desirable combinationof these methods.

Almost any typical fugitive carrier liquid may be used, depending onplate fabricating parameters, including isopropanol, ethyl alcohol,trichloroethylene, naphtha, other volatile organic liquids, water and soon. Mixtures of from about 10% to about 20% by weight graphite have beenfound to be generally suitable for coating.

Non-fugitive carrier liquids found to be useful herein include mineraloil, petroleum oil, castor oil, polyglycols and mixtures thereof. On agraphite/liquid carrier dry weight basis the useful range ofpigmentation extends from about 50% to about The interfacial layer ofthis invention may have any suitable thickness but in order to achievethe dual properties preferred of electrical conductivity yet electroniccharge carrier blocking to prevent excessive dark, decay when conductivesupport bases are used, the interfacial layer should preferably have athickness substantially uniform over the effective surface of thexerographic plate to assure uniform xerographic characteristics,desirably of from about 1 to about 20 microns with a preferred rangebeing from about 1 to about 5 microns.

The graphite-liquid carrier slurry may be applied to the belt base byany of the well known painting or coating methods including spraying,flow coating, knife coating, electrostatic coating, dip coating, reverseroll coating and so on. After or during the drying of this interfaciallayer the photoconductor may be applied thereover by any suitable methodsuch as vacuum evaporation for amorphous selenium or any of the abovecoating methods for the resin based phthalocyanine binder system.

In addition, methods of depositing a thin layer of graphite other thanusing a carrier liquid may be used such as doctor blading or draw downbar coating particulate graphite itself onto a belt base optionallyrendered tacky to adhesively receive the particles.

Layer 7 may comprise any suitable photoconductive insulating material.Amorphous selenium alone or alloyed with arsenic, tellurium, antimony,bismuth, etc., or amorphous selenium or its alloys doped with halogens,for example, is found to be a preferred photoconductive insulatingmaterial for use herein because of a surprisingly and completelyunexpected increased adherence to substrates when deposited on thegraphite interfaces of this invention. Amorphous selenium is, of course,also preferred because of its excellent photoconductive insulatingproperties including its extremely high quality image making capability,low fatigue, high light response and capability to receive and retaincharge areas at different potentials and of different polarities.Phthalocyanine pigmented organic binder photoconductors, for example, asdescribed in copending application Ser. No. 375,191, filed June 13,1964, are also preferred for use herein, generally, for the samereasons. An especially preferred phthalocyanine pigment is x-formmetal-free as described in copending application Ser. No. 505,723, filedOct. 29, 1965, now US. Pat. 3,357,989.

Generally, the thickness of the photoconductor will depend upon theparticular photoconductor and on the desired xerographic properties ofthe resultant plate. However, for thicker amorphous seleniumphotoconductor layers, for example, much greater than 40 microns used inflexible plate, i.e., belt configurations it is found that the beam likeflexing forces induced in the photoconductive layer itself, as a resultof extreme bending, tend to fracture the photoconductor regardless ofthe type of substrate or interface used. But it is found that in aflexible plate configuration amorphous selenium layers up to about 35microns in thickness deposited onto the interfacial layer of thisinvention show superb adhesion. For rigid backed plate configurationsthe thickness of the amorphous selenium will primarily depend on thedesired xerographic properties of the resultant plate with a preferredthickness range of from about 20 to about 80 microns. The thickness ofthe phthalocyanine binder photoconductor for rigid and flexible platesis desirably between about one to about 100 microns and preferably inabout the five 30 micron range.

However any suitable photoconductive insulating material may be used incarrying out the invention. Typical photoconductors include: alloys ofsulfur with selenium, selenium doped with materials such as thallium,cadmium sulfide, cadmium selenide, etc., particulate photoconductivematerials such as zinc sulfide, zinc cadmium sulfide, French processzinc oxide, phthalocyanine, cadmium sulfide, cadmium selenide, zincsilicate, cadmium sulfoselenide, linear quinacridones, etc. dispersed inan insulating inorganic film forming binder such as a glass or aninsulating organic film forming binder such as an epoxy resin, asilicone resin, an alkyd resin, a styrene-butadiene resin, a wax or thelike. Other typical photoconductive insulating materials include:blends, copolymers, terpolymers, etc. of photoconductors andnon-photoconductive materials which are either copolymerizable ormiscible together to form solid solutions and organic photoconductivematerials of this type include: anthracene, polyvinyl-anthracene,anthraquinone, oxidiazole derivatives such as 2,5 bis (p-aminophenyl-l),1,3,4-oxidiazole; 2-phenylbenzoxazole; and charge transfer complexesmade by complexing resins such as polyvinylcarbazole, phenolaldehydes,epoxies, phenoxies, polycarbonates, etc., with Lewis acid such asphthalic anhydride; 2,4,7-trinitrofluorenone; metallic chlorides such asaluminum, zinc or ferric chlorides; 4,4-bis(dimethylamino) benzophenone;chloranil; picric acid; 1,3,5-trinitrobenzene; l-chloroanthraquinone;bromal; 4-nitro-benzaldehyde; 4-nitrophenol; acetic anhydride; maleicanhydride; boron trichloride; maleic acid, cinnamic acid; benzoic acid;tartaric acid; malonic acid and mixtures thereof.

Referring now to the figure, in operation, xerographic plate 12 in theform of a flexible endless belt is advanced in a clockwise direction bydrive roller '10 powered by motor 13 around guide and tension roller 11,the belt advanced sequentially past corona charging device 15, exposurestation 17, developing station 19 to be transferred to support surface25 in the region of corona discharge device 26, and finally pastrotating brush 27 to clean and ready the surface of the xerographicplate for a new cycle of operation.

The corona discharge device 15 is a preferred mech anism for sensitizingthe xerographic plate before exposure which sensitization consists ofimparting a uniform charge to the surface of the photoconductor. Twoexamples of corona discharge devices are disclosed in Vyverberg Pat.2,836,725 and Walkup Pat. 2,777,957. The plate 12 is preferably chargedwhen it is at its highest insulating value, i.e., in the absence ofactinic radiation or in the dark. After charging, the plate advances toexposure station 17 where light rays 21 from an original, preferablysynchronized to the movement of the xerographic plate by conventionalapparatus not shown, selectively discharges the xerographic plate inaccordance with the intensity of the actinic radiation reaching theplate, thereby leaving on the plate as it advances towards roller 10 alatent electrostatic image coiresponding to the image of the original.

Other methods of forming a latent image are available in the art andinclude latent image transfer techniques 8 for example see Carlson Pats.2,982,647 and 2,825,814 and by the use of shaped electrodes or pinmatrices, for example see Schwertz Pats. 3,023,731 and 2,919,967 and byelectron beam techniques, for example see Glenn Pat. 3,1 13,179.

The latent electrostatic images may be rendered visible by any suitabledeveloping means known to those skilled in the art and illustratively bythe form of cascade development as illustrated which generally consistsof gravitationally flowing developer material 33 consisting of a twocomponent material of the type disclosed for example in Walkup et a1.Pat. 2,638,416 over the xerographic plate bearing the latent image. Thetwo components consist of an electroscopic powder termed toner and agranular material called carrier and which by mixing acquiretriboelectric charges of opposite polarities. In development the tonercomponent usually oppositely charged to the latent image is deposited onthe latent electrostatic image to render that image visible. Inoperation developer material 33 is carried by a conveyor 34 to chute 32with gate 30 to regulate the flow of developer down the chute to cascadein contact with the latent electrostatic image. The developer afterpassing over the latent electrostatic image passes into developerreservoir 36 where it may be used over again with allowance made toreplenish the amount of toner left behind on the xerographic plate.

The loosely adhering xerographic powder image 37 formed on the surfaceof plate 12 during development is then advanced contiguous to transferweb 25 where the loose powder image is transferred to the web andaifixed thereto by any suitable means such as solvent vapor or heatfusing. The permanitized image is then rolled onto takeup roll 35 whereit is stored until ready for use.

By using interface 8, the resistance of the plate to cracking andspalling of the photoconductor caused by flexing and other strains isfound to be greatly enhanced. Although the theory of operationexplaining why layer 8 provides for this improved result is notcompletely understood, it is thought that the thin graphite interfaceacts as an excellent and outstanding tie coat because slippage in thegraphite interlayer permits the selenium or other photoconductiveinsulating material to be bent without excessive strain on theinterface. It is thought that the effect is almost surely due to thegraphite pigment, and not the relatively trivial proportion or binderwhich may be found in some of the preferred embodiments of the inventiveinterlayers hereof.

The following examples further specifically define the inventiveinterfacial layer and the novel xerographic plate one embodiment ofwhich is shown in the figure as plate 12. The parts and percentages areby weight unless otherwise indicated. The examples below are intended toillustrate various preferred embodiments of the inventive interfaciallayer and xerographic plate and process of making and using same of thisinvention. In each example a qualitative tape test is performed byapplying pressure sensitive adhesive tape such as Scotch brand pressuresensitive Magic transparent tape No. 810 to the bonded photoconductorsurface for testing the adherence of the photoconductive insulator tothe underlying belt. The strip of tape is snapped off the photoconductorby a quick movement of the hand to give a quick but rather severe testof adhesion, since insufiiciently bonded material will be pulled offeither in part or in total. Also, in each example a qualitative flextest is performed by bending the specimen once over a 1 inch diametersteel bar and carefully observing for any spalling of or microcracks inthe photoconductor surface.

Xerographic prints are made using the sample specimens in the example bytaping the test specimens on a rigid xerographic drum and performing thesequential xerographic operations generally described herein.

Except where otherwise provided, the test specimen is xerographicallyprocessed with positive charging, the exposure being from a tungstenfilament lamp operating at a filament temperature of about 2950 K., atan exposure 9 level at the photoconductor surface in illuminated areasof about 3.2 f.c.s. to form a latent electrostatic image which is thencascade developed. The clean, sharp image thus produced is transferredto a receiving sheet and fused to produce a high quality xerographicimage.

Each test specimen holds up under the tape and flex tests better than acontrol plate constructed according to the example but absent theinventive graphite interlayer. Also the control plate exhibits inferiorxerographic properties, especially lacking the ability to effectivelydissipate charge in illuminated areas in Examples I and III whereelectrically insulating substrates are used.

Example I About a 3 mil thick Mylar film is dip coated into a colloidalgraphite dispersion in mineral spirits with a solid content of about 10percent available under the designation dag Dispersion No. 2404 from theAcheson Colloids Co. The Mylar film is removed and dried for about 1hour at about 100 C. to form about a micron layer on top of the Mylar.The surface resistivity of the coated film is measured laterally to beabout 4 /2 10 ohms/sq.

An epoxy-phenolic electrically insulating organic'binder resin is thenprepared by mixing together about 35 /2 parts of a solid synthetic epoxyresin possessing terminal epoxide groups available under the trademarkEpon 1007 from Shell Chemical Corp., about 20 parts of a phenolic bakingtype coating intermediate containing about 75 percent non-volatilematter and available under the trademark Methylon 75201 from the GeneralElectric Co., about 4 /2 parts of a urea-melamine formaldehyde resin inan organic solvent available under the trademark Uformite F-24O from theRohm & Haas Co. containing about 60 percent non-volatile matter, about40 parts of the organic solvent ethylene glycol monoethyl etheravailable under the trademark Cellosolve from the Union Carbide Corp. toform a mixture of about 53 percent non-volatile solids.

About 11 /2 parts of the epoxy-phenolic mixture of about 53 percentnon-volatile solids, about 1 part of X- form metal-free phthalocyanineprepared as described in copending application Ser. No. 505,723, filedOct. 29, 1965 and about parts of ethylene glycol monoethyl etheravailable under the trademark Cellosolve from the Union Carbide Corp.are put together and ball milled in about a 4 fluid ounce glass jarcontaining about 70 parts of 4; inch steel shot and milled for about 1hour. The

resulting dispersion is then coated over the interfacial layer on theMylar film and dried to a thickness of about microns.

Example 11 A colloidal graphite conductive pigmented dispersioncontaining about 20 percent solids in an organic fugitive carrier ofisopropanol available under the designation dag Dispersion No. 154 fromAcheson Colloids Corp. is coated onto about an 8 mil thick flexiblebrass foil substrate and allowed to dry in air to form a layer ofgraphite about 1 to 2 microns thick.

About a 20 micron layer of amorphous selenium is then vacuum evaporatedover the thin layer of graphite as more fully described in Bixby Pat.2,970,906.

The plate holds a 20 volt/micron positive charge indicating the fineblocking characteristics of the graphite layer and shows a typicalselenium photoresponse during xerographic processing. This plateexhibits outstanding adhesion and flexing properties. This plate showssuch exceptional adhesion to the substrate that even when flexed arounda pipe of inch diameter, no microcracks are observed.

Example IH Example H is followed except that about an 8 milpolycarbonate film substrate is used in place of the flexible brass foilsubstrate.

This plate also exhibits excellent adhesion, flexing and xerographicproperties.

10- Example IV Example H is followed except that about a 45 micron layerof amorphous selenium is vacuum evaporated over the graphite.

A control plate absent the graphite interlayer is prepared and bothplates are xerographically cycled on a drum reveloving at about 13.3r.p.m. Exposures are at about 30 f.c.s. from a white fluorescent lamp.Both plates are charged positively to an initial value of about 800volts. Both plates are sequentially charged and discharged for 150cycles and then percentage dark discharge of both plates is measured 30seconds after charging and no exposure. The control plate has a fatigueddark discharge 30 seconds after charging, after 150 rapid cycles ofcharge and discharge of about 8 percent and the inventive plate,although not as low as the control, compares favorably with a darkdischarge of about 15 percent which is certainly not excessive. However,a tremendous advantage in lower residual build up is found for inventiveplate. The control plate after about 60 cycles, built up and maintainedfor further cycles a residual potential of about volts while theinventive plate more slowly built up and maintained for further cycles aresidual potential of about only 30 volts. This marked advantage oflower residual potential for the inventive plate manifested itself inlower background, higher contrast copies than those produced on thecontrol plate.

Selenium adhesion to the graphite interlayer of the above plate isexcellent, i.e., no selenium is removed by the tape. The plate issuccessfully flexed around a three inch diameter roll without anyevidence of cracking or spalling in the selenium layer. The inventiveplate exhibits a photosensitivity comparable to the control plate.

The adhesion of selenium coated direcfly on brass is poor, particularlyunder flexing conditions. Considerable cracking and spalling occurs whenthe control selenium plate is flexed around a three inch diameter roll.

Thus, the graphite interlayer of this invention confers unexpectedlyexcellent adhesion, flexing, and physical blocking conditions to theselenium-brass interface with a dramatically lower residual potential.

Example V Example H is followed except that about a 5 mil flexiblealuminum substrate is used.

Although specific components and proportions have been stated in theabove description of preferred embodiments of the interfacial layer asused in the fabrication of a xerographic plate and its use, there are,as disclosed herein, other suitable materials which may be used withsimilar results. In addition, other materials may be added to themixture or variations made in the various fabrication and processingsteps to synergize, enhance or otherwise modify the properties of theresultant xerographic plate. For example various plasticizers andmoisture and other proofing agents may be added to the various polymericsubstrates mentioned herein.

It will be understood that various other changes in the details,materials, steps and arrangements of parts which have been hereindescribed and illustrated in order to explain the nature of theinvention will occur to and may be made by those skilled in the art upona reading of this disclosure and such changes are intended to beincluded within the principleand scope of this invention.

What is claimed is:

1. A flexible photoconductive member resistant to spalling, cracking,and micro-cracking upon curvature in a substantially circularconfiguration having a diameter of at least inches, comprising:

(a) a flexible electrically conductive metallic support base;

(b) an interface comprising predominantly graphite overlying saidsupport base; and

(c) an amorphous photoconductive insulating layer comprising amorphousselenium overlying said inter-' face opposite said support base.

2. A photoconductive member according to claim 1 wherein said interfaceis between 1 and 20 microns thick.

3. A photoconductive member according to claim 2 wherein said interfaceis between about 1 and about 5 microns thick.

4. A photoconductive member according to claim 2 wherein the electricalresistivity of said interface is less than about 10 ohm-centimeters.

5. A photoconductive member according to claim 1 wherein said interfaceconsists essentially of free graphite.

6. A photoconductive member according to claim 1 wherein said interfacecomprises, by weight, from about 50% to about 80% graphite.

7. An electrophotographic process wherein the photoconductive member ofclaim 1 is provided with a latent electrostatic image and developed withelectrically attractable marking particles.

8. An electrophotographic process according to claim 7 wherein thelatent electrostatic image is provided by electrically charging saidmember and then exposing the charged member to a light image pattern tobe reproduced.

References Cited UNITED STATES PATENTS 3,243,293 3/1966 Stockdale 96-1.5X 3,655,371 4/1972 Chafaris 96-1.5 X 3,639,121 2/1972 York 117-226 XFOREIGN PATENTS 1,008,633 11/ 1965 Great Britain 96-1.5 1,062,092 3/1967 Great Britain 96-1.5 234,016 8/ 1959 Australia 96-1.5

NORMAN G. TORCHIN, Primary Examiner J. R. MILLER, Assistant ExaminerU.S. Cl. X.R.

